Investigation of the elastic properties of LiKSO4 single crystals as a function of temperature and pressure

Abu-Kharma, Mahmoud (2002) Investigation of the elastic properties of LiKSO4 single crystals as a function of temperature and pressure. Masters thesis, Memorial University of Newfoundland.

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Abstract

The ultrasonic pulse-echo method is used to study the elastic properties of LiKSO4 single crystals as a function of temperature between 4 K and 300 K and at pressures up to 7 kbar. The measured values of the elastic constants obtained at room temperature for the hexagonal phase structure are: C66 = 1.41 ± 0.03, C44 = 2.11 ± 0.04, C11 = 5.7 ± 0.1, C12 = 2.92 ± 0.06, and C33 = 6.7 ± 0.1 (×1010 N/m). At ambient pressure, phase transitions between 130 K and 300 K have been detected using the measurement of the relative change in sound velocity Δv/v in both x- and z-directions for longitudinal modes. First order transitions are observed around 195 K and 185 K on cooling, and around 195 K and 260 K on heating. Relying on the measurements of Δ v/v in the x-direction for longitudinal modes in the same temperature range at different pressures, we derive the pressure-temperature phase diagram. The main features obtained for this diagram are: we observe a triple point at (1.8 kbar, 200 K) during the cooling process that shifts to (5 kbar, 286 K) for the heating, the intermediate phase PIV vanishes beyond the triple point, and the transition temperature is shifted to higher values with increasing pressures. In the temperature region below 130 K, we observed at low pressures phase transitions at 35 K and 65 K, with no sign of thermal hysteresis. However, for pressures greater than 3.2 kbar the transition observed at 35 K is suppressed. The existence of the phases PIII, PIV, PV, PIX and PX were confirmed. There were no transitions observed at 165 K, 135 K and 80 K, so we cannot confirm the PVI, PVII and PVIII phases.

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